Week question am I 5 or 4 weeks?

Jessicadbaker

I haven't had a baby in well almost 8 years LOL! So I'm re learning all this awesome info. ;-). My question is how come according to my doctor I am 5 weeks pregnant but on The Bump when I put my 1st day of my last AF it says I'm 4 weeks. Does The Bump start counting a week after your AF? I assum so I'm just confused which one I should go by when reading info. about me and baby to be's progress.